A COMBUSTION MODE SWITCHING CONTROL SYSTEM FOR A DIESEL ENGINE AND A METHOD OF SWITCHING BETWEEN A PREMIXED COMPRESSION IGNITION AND A DIESEL COMBUSTION MODE

Abstract

A combustion mode switching control system for diesel engines is provided. The system includes: a switch determination module that initiates a switch request to switch between at least one of a premixed compression ignition (PCI) mode and a diesel combustion mode based on engine speed and at least one of fuel quantity and torque; a transition module that commands the at least one of the PCI mode and the diesel combustion mode based on the switch request; and a control module that controls at least one of target airflow, desired fuel quantity, and desired fuel injection timing based on the command.

Full Text

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GP-307078-PTE-CD
DIESEL COMBUSTION MODE SWITCHING
CONTROL STRATEGY AND MODEL
FIELD OF THE INVENTION
[0001] The present disclosure relates to methods and systems for
controlling fuel injection of a diesel combustion engine.
BACKGROUND OF THE INVENTION
[0002] The statements in this section merely provide background
information related to the present disclosure and may not constitute prior art.
[0003] Traditionally, there have been two primary forms of
reciprocating piston or rotary internal combustion engines: diesel and spark
ignition engines. While these engine types have similar architecture and
mechanical workings, each has distinct operating properties. For example, to
initiate combustion, spark ignition engines supply an air/fuel mixture to the
engine cylinder while controlling spark timing. In contrast, diesel engines
compress air in the cylinder while controlling fuel injection timing to initiate the
start of combustion.
[0004] One of the major advantages that the diesel engine has over
the pre-mixed charge spark-ignited engine is higher thermal efficiency. This is
generally due to the higher compression ratio and leaner combustion
operation provided by the diesel engine. One trade-off to the higher thermal
efficiency of the diesel engine is that it is more difficult or expensive to achieve
the same tailpipe NOX emission levels as does the spark-ignited engines.
This is due to the lean air/fuel control nature of the diesel engine.

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[0005] Premixed Compression Ignition (PCI) is an advanced diesel
combustion technique that has great potential for reducing diesel engine
emissions. With PCI, fuel is injected into the combustion chamber of the
cylinder much earlier in the combustion stroke than would be done for diesel
combustion. The desired fuel amount is supplied significantly before the
piston reaches the compression top dead center (TDC). The early injected
fuel is mixed sufficiently with the air before the piston reaches the
compression TDC. Thus, the technique provides a lean and well mixed state
of the air/fuel mixture before ignition.
[0006] However, PCI combustion is limited to low-load operating
conditions. Therefore, during other operating conditions diesel combustion is
required. Because PCI combustion and diesel combustion have different
requirements for the exhaust gas recirculation (EGR) percentage, the air/fuel
ratio, and the fuel injection timing, the problem of how to switch smoothly
between these two combustion modes becomes a concern. Excessive
smoke, NOX, and combustion noise will result from lack of effective
combustion mode switching control.
SUMMARY OF THE INVENTION
[0007] Accordingly, a combustion mode switching control system for
diesel engines is provided. The system includes a switch determination
module that initiates a switch request to switch between at least one of a
premixed compression ignition (PCI) mode and a diesel combustion mode
based on engine speed and at least one of fuel quantity and torque. A
transition module commands at least one of the PCI mode and the diesel
combustion mode based on the switch request. A control module controls at
least one of target airflow, desired fuel quantity, and desired fuel injection
timing based on the command.

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[0008] In other features, a method of switching between a premixed
compression ignition mode (PCI) and a diesel combustion mode for diesel
engines is provided. The method includes: initiating a switch request to
switch between at least one of a premixed compression ignition (PCI) mode
and a diesel combustion mode based on engine speed and at least one of
fuel quantity and torque; commanding at least one of the PCI mode and the
diesel combustion mode based on the switch request; and controlling at least
one of target airflow, desired fuel quantity, and desired fuel injection timing
based on the commanded mode.
[0009] Further areas of applicability will become apparent from the
description provided herein. It should be understood that the description and
specific examples are intended for purposes of illustration only and are not
intended to limit the scope of the present disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The drawings described herein are for illustration purposes
only and are not intended to limit the scope of the present disclosure in any
way.
[0011] Figure 1 is a functional block diagram of a diesel engine.
[0012] Figure 2 is a cross-sectional view of a cylinder of a diesel
engine.
[0013] Figure 3 is a dataflow diagram of a diesel combustion mode
switching control system.
[0014] Figure 4 is a diagram illustrating mode transitions.
[0015] Figure 5 is a state transition diagram illustrating the
coordination of combustion mode switching.
[0016] Figure 6 illustrates an exhaust gas recirculation control
model.
[0017] Figure 7 is illustrates a torque control model.

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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] The following description is merely exemplary in nature and
is not intended to limit the present disclosure, application, or uses. It should
be understood that throughout the drawings, corresponding reference
numerals indicate like or corresponding parts and features. As used herein,
the term module refers to an application specific integrated circuit (ASIC), an
electronic circuit, a processor (shared, dedicated, or group) and memory that
executes one or more software or firmware programs, a combinational logic
circuit, and/or other suitable components that provide the described
functionality.
[0019] Referring now to Figure 1, an exemplary diesel engine
system 10 is schematically illustrated. It is appreciated that the diesel engine
system 10 is merely exemplary in nature and that the diesel combustion mode
switching control strategy described herein can be implemented in various
diesel engine systems. The diesel engine system 10 includes a diesel engine
12, an intake manifold 14, a common rail fuel injection system 16 and an
exhaust system 18. The exemplary engine 12 includes six cylinders 20
configured in adjacent cylinder banks 22,24 in V-type layout. Although Figure
1 depicts six cylinders (N = 6), it can be appreciated that the engine 12 may
include additional or fewer cylinders 20. For example, engines having 2, 4, 5,
8, 10, 12 and 16 cylinders are contemplated.
[0020] Air is drawn into the intake manifold 14, is distributed to the
cylinders 20 and is compressed therein. Figure 2 illustrates a cylinder 20 in
more detail. Fuel is injected into an intake port 31 of the cylinder 20 and/or
directly into the cylinder 20 by the common rail injection system 16 (Figure 1).
The heat of the compressed air ignites the air/fuel mixture. An intake valve 32
selectively opens and closes to enable the air to enter the cylinder 20. The
intake valve position is regulated by an intake camshaft (not shown). A fuel
injector 33 injects fuel into the cylinder 20. The fuel injector 33 is controlled to
provide a desired air-to-fuel (A/F) ratio within the cylinder 20 at a time and
quantity determined by the diesel combustion mode switching control

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strategy. An additional fuel injector shown in phantom at 34 may be provided
at or near the intake port 31 of the cylinder 20 and may be similarly controlled
according to the diesel combustion mode switching control strategy.
[0021] A piston 35 compresses the A/F mixture within the cylinder
20. The compression of the hot air ignites the fuel in the cylinder 20, which
drives the piston 35. The piston 35, in turn, drives a crankshaft (not shown) to
produce drive torque. Combustion exhaust within the cylinder 20 is forced out
an exhaust port 36 when an exhaust valve 37 is in an open position. The
exhaust valve position is regulated by an exhaust camshaft (not shown).
Although single intake and exhaust valves 32,37 are illustrated, it can be
appreciated that the engine 12 can include multiple intake and exhaust valves
32,37 per cylinder 20.
[0022] Referring back to Figure 1, the exhaust gases are exhausted
from the cylinders 20 and into the exhaust system 18. The exhaust system 18
includes exhaust manifolds 28,30, exhaust conduits 27,29 a catalyst 38, and a
diesel particulate filter (DPF) 40. First and second exhaust segments are
defined by the first and second cylinder banks 22,24. The exhaust manifolds
28,30 direct the exhaust segments from the corresponding cylinder banks
22,24 into the exhaust conduits 27,29. In some instances, the diesel engine
system 10 can include a turbo 26 that pumps additional air into the cylinders
20 for combustion with the fuel and air drawn in from the intake manifold 14.
The exhaust is directed into the turbo 26 to drive the turbo 26. A combined
exhaust stream flows from the turbo 26 through the catalyst 38 and the DPF
40. The DPF 40 filters particulates from the combined exhaust stream as it
flows to the atmosphere.
[0023] In some instances, the diesel engine system can include an
exhaust gas recirculation (EGR) system (not shown). An EGR system
includes an EGR valve (not shown) that regulates exhaust flow back into the
intake manifold 14. The mass of exhaust that is circulated back into the
intake manifold 14 assists to reduce the temperature of the air in the manifold
14 and affects engine torque output.

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[0024] A controller 42 regulates operation of the diesel engine
system 10 according to the diesel combustion mode switching control strategy
of the present disclosure. . More particularly, the controller 42 determines if a
switching between PCI and conventional diesel combustion is desired and
controls the engine to switch between the combustion modes accordingly.
The controller 42 communicates with an intake manifold boost pressure
(boost) sensor 44, a mass airflow (MAF) sensor 45, an engine speed sensor
46, and an intake manifold temperature sensor 47. The boost sensor 44
generates a signal indicating the air pressure within the intake manifold 14.
The MAF sensor 45 generates a MAF signal based on the flow of air into the
engine 12. The engine speed sensor 46 generates a signal indicating engine
speed (RPM). The intake manifold temperature sensor 47 generates a
temperature signal based on the temperature of air in the intake manifold 14.
An exhaust pressure sensor 48 generates an exhaust pressure signal based
on pressure of the exhaust flowing from the turbo 26.
[0025] Referring now to Figure 3, a dataflow diagram illustrates an
embodiment of a diesel combustion mode switching control system 49 that
may be embedded within the controller 42. Various embodiments of diesel
combustion mode switching control systems 49 according to the present
disclosure may include any number of sub-modules embedded within the
controller 42. The sub-modules shown may be combined and/or further
partitioned to similarly control the combustion mode. In various embodiments,
the controller 42 of Figure 3 includes a switch determination module 50, a
transition module 52, an air/EGR estimation module 54, and an air/fuel control
module 56.
[0026] The switch determination module 50 receives as input
engine operating parameters such as engine speed 58 and an actual fuel
quantity 57 (determined by other sub-modules within controller 42). The
switch determination module 50 determines whether a transition between the
PCI mode and the diesel combustion mode is desired based on the engine
operating parameters. If a transition is desired, the switch determination

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module 50 outputs a switch request 60 to the transition module 52. The
air/EGR estimation module 54 receives as input engine operating parameters
such as engine speed 58, the actual fuel quantity 57, mass airflow 70, boost
pressure in the intake manifold 72, temperature in the intake manifold 74, and
exhaust pressure 76. The air/EGR estimation module 54 determines if the
air/EGR requirement for the PCI or diesel combustion is met. The air/EGR
requirement estimation module outputs an air/EGR condition 78 to the
transition module 52.
[0027] The transition module 52 receives as input the switch
request 60 and the air/EGR condition 78. The transition module 52
coordinates when and how to transition between the combustion modes
based on the conditions of air (if going to diesel combustion) or EGR (if going
to PCI). Once the transition module 52 determines the proper mode to
transition to, a desired mode 80 is output to the air/fuel control module 56.
The air/fuel control module 56 receives as input the mode 80 and engine
operating parameters such as engine speed 58, actual fuel quantity 57, mass
airflow 70, actual injection time 82, and desired torque 84. The air/fuel control
module 56 determines how to control transitions between modes and during
operation in the PCI mode and the diesel combustion mode. More
specifically, the air/fuel control module 56 controls the air target 86, fuel
injection quantity 88, and the desired timing 90. The details of the diesel
combustion mode switching control system 49 will be described in more detail
below.
[0028] Referring now to Figure 4, the switch determination module
50 of Figure 3 will be discussed in more detail. The switch determination
module 50 determines if a switching between the PCI mode and the diesel
combustion mode is desired. The strategy is designed to optimize the goals
of minimizing the switching between the two combustion modes and
maximizing the PCI combustion time to take advantage of the low emission
levels of PCI combustion.

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[0029] Figure 4 depicts five engine operating point transition
scenarios labeled A-E. Operating conditions of the engine are divided into
three combustion modes: the diesel combustion mode 100, the PCI mode
102, and the hysteresis or transitional mode 104. The switch request 60 is
determined based on fuel quantity shown along the y-axis at 106 and engine
speed shown along the x-axis at 108. In an alternative embodiment, the
switch request 60 is determined based on torque and engine speed. The
strategy for determining the switch request 60 is based on the transition
scenarios as described below.
[0030] Scenario A illustrates the fuel and speed requirements for
when the combustion mode remains in the hysteresis area between the PCI
and the diesel combustion modes (no switching occurs). Scenario B
illustrates the fuel and speed requirements for when the combustion mode
switches from the diesel combustion mode 100 to the PCI mode 102 and
remains in the PCI mode 102 for some time. Scenario C illustrates the fuel
and speed requirements for when the combustion mode switches from the
PCI mode 102 to the diesel combustion mode 100 and remains in the diesel
combustion mode 100 for some time.
[0031] Scenario D illustrates the fuel and speed requirements for
when the combustion mode switches from the diesel combustion mode 100 to
the PCI mode 102 then switches back to the diesel combustion mode 100
after only being in the PCI mode 102 for a short period of time. Upon
determination of this scenario, the transition is actually limited to stay in the
diesel combustion mode 100 for a certain delay period (no actual switching
occurs). During this scenario, the switch request 60 is properly set to reflect
this limitation. This prevents unnecessary switching back and forth to PCI
combustion for only short periods of time.
[0032] Scenario E illustrates the fuel and speed requirements for
when the combustion mode will switch from the PCI mode 102 to the diesel
combustion mode 100 and then switch back to the PCI mode 102 after only
being in the diesel combustion mode 100 for a short period of time. In this

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case the switching must occur. This is due to the fact that PCI combustion
may only be operated during low load operating conditions.
[0033] Referring now to Figure 5, the transition module 52 of
Figure 3 will be discussed in more detail. Because the operating condition
requirements for PCI and diesel combustion are very different, it is impractical
to switch from one mode to the other immediately after a mode switch request
60 is issued. Therefore, when the mode switch request 60 is submitted to the
transition module 52, the transition module 52 will coordinate the combustion
mode switching at the right moment and under the appropriate conditions.
The transition module 52 includes a Combustion Mode Switching
Coordination Subsystem (CMSCS) which performs this functionality.
[0034] As shown in the state diagram of Figure 5, when the CMSCS
receives a switch request 60 to switch to a different combustion mode, the
mode will first be set to a transitional mode. The transitional mode can be at
least one of a diesel combustion to PCI transition mode 110 and a PCI to
diesel combustion transition mode 112. For example, if the initial mode is the
diesel combustion mode 100, after receiving a switch request 60 to switch to
the PCI mode 102, the CMSCS will switch the mode to the diesel combustion
to PCI transition mode 110. While in this mode, the CMSCS will check the
air/EGR condition received from the air/EGR estimation module 54 of Figure
3. If the air/EGR condition indicates EGR is sufficient, the CMSCS switches
the mode to the PCI mode 102. Otherwise, if a switch request to switch back
to the diesel combustion mode 100 is received before the air/EGR condition
78 indicates the EGR is ready, the CMSCS switches the mode back to the
diesel combustion mode 100. This strategy guarantees that the desired
combustion mode is entered only when appropriate conditions such as air and
EGR percentages are achieved.

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[0035] Similarly, if the initial mode is the PCI mode 102, after
receiving a switch request 60 to switch to the diesel combustion mode 100,
the CMSCS will switch the mode to the PCI to diesel combustion transition
mode 112. While in this mode, the CMSCS will check the air/EGR condition
received from the air/EGR estimation module 54 of Figure 3. If the air/EGR
condition indicates the air/EGR is sufficient, the CMSCS will switch the mode
to the diesel combustion mode 100. Otherwise, if a switch request 60 to
switch back to the PCI mode 102 is received before the air/EGR condition 78
indicates the air/EGR is ready, the CMSCS will switch the mode back to the
PCI mode 102.
[0036] Referring now to Figure 6, the air/EGR estimation module 54
of Figure 3 will be discussed in more detail. This subsystem includes a real
time predictive estimation sub-module 120 and a target comparison sub-
module. The estimation sub-module 120 estimates a percentage of EGR and
a percentage of oxygen in the intake manifold based on various measurement
parameters such as engine speed, mass airflow, fuel quantity, boost pressure,
intake temperature, and exhaust pressure. The target comparison sub-
module 122 computes a target value and compares the estimated EGR and
oxygen percentages to the target value to determine if the air/EGR
requirements for PCI or diesel combustion are met. An air/EGR condition is
set based on whether the requirements are met. The air/EGR condition is
output to the transition module 52 of Figure 3 to determine the appropriate
combustion mode to command for the engine.
[0037] Referring now to Figure 7, the air/fuel control module 56 of
Figure 3 will be discussed in more detail. This subsystem controls air and
fuel to the cylinder to achieve smooth transitions during combustion mode
switching. The air/fuel control module 56 determines target values for mass
airflow, fuel injection quantity, and fuel injection timing based on the mode
determined by the transition module 52 of Figure 3. During the PCI mode and
the diesel combustion mode, the mass airflow, the fuel injection quantity, and
the fuel injection timing is determined based on the engine speed and fuel

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quantity (or torque). In an exemplary embodiment separate mass airflow, fuel
injection quantity, and fuel injection timing lookup tables are implemented for
each mode. The lookup tables may be implemented as two-dimensional
tables with engine speed and fuel quantity (or torque) as the indices.
[0038] During the transition modes, the mass airflow target and the
desired fuel injection timing are determined based on the engine speed and
the fuel quantity (or torque). In an exemplary embodiment separate mass
airflow and fuel injection timing lookup tables are implemented for each
transition mode. The lookup tables may be implemented as two-dimensional
tables with engine speed and fuel quantity (or torque) as the indices.
However, the torque control sub-system shown in Figure 7 is adopted to
adjust the fuel injection quantity during the transition modes so that the
desired torque is maintained and a smooth transition between combustion
modes is achieved.
[0039] In Figure 7, a torque estimation sub-module 124 determines
an estimated torque based on the combustion mode, fuel quantity, mass
airflow, injection time, and engine speed. The estimated torque is subtracted
from a determined desired torque at 126. An inverse torque sub-module 128
determines a fuel adjustment value based on the difference in torque and
other engine operating parameters such as engine speed, estimated torque,
and combustion mode. The fuel adjustment value is then added to the actual
fuel quantity at 130 and output as a desired fuel quantity. The desired fuel
quantity is then used to control fuel to the cylinder.
[0040] Those skilled in the art can now appreciate from the
foregoing description that the broad teachings of the present disclosure can
be implemented in a variety of forms. Therefore, while this disclosure has
been described in connection with particular examples thereof, the true scope
of the disclosure should not be so limited since other modifications will
become apparent to the skilled practitioner upon a study of the drawings,
specification, and the following claims.

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CLAIMS
What is claimed is:
1. A combustion mode switching control system for diesel engines,
comprising:
a switch determination module that initiates a switch request to
switch between at least one of a premixed compression ignition (PCI) mode
and a diesel combustion mode based on engine speed and at least one of
fuel quantity and torque;
a transition module that commands the at least one of the PCI
mode and the diesel combustion mode based on the switch request; and
a control module that controls at least one of target airflow,
desired fuel quantity, and desired fuel injection timing based on the command.
2. The system of claim 1 further comprising an air estimation
module that determines a current status of air flowing into the engine and
wherein the transition module commands the at least one of the PCI mode
and the diesel combustion mode based on the status.
3. The system of claim 2 wherein the air estimation module
determines the current status of the airflow based on whether a percentage of
air flowing from exhaust gas recirculation (EGR) is sufficient to allow a switch
to occur.
4. The system of claim 2 wherein the air estimation module
determines the current status of the airflow based on at least one of fuel
quantity, torque, engine speed, mass airflow, boost pressure in the intake
manifold, temperature in the intake manifold, and exhaust pressure.

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5. The system of claim 2 wherein the transition module commands
at least one of a diesel combustion to PCI transition mode and a PCI to diesel
combustion transition mode after receiving the switch request and until at
least one of the status indicates that the airflow is sufficient to accommodate
the switch request and a subsequent switch request is received indicating to
switch back to a previous mode.
6. The system of claim 1 wherein the control module controls
target airflow, desired fuel injection quantity, and desired fuel injection timing
based on the mode, engine speed, and at least one of actual fuel injection
quantity and torque.
7. The system of claim 6 wherein the control module controls
target airflow, desired fuel injection quantity, and desired fuel injection timing
during the PCI mode and the diesel combustion mode based on separate
target airflow, desired fuel injection quantity, and desired fuel injection timing
lookup tables for each of the PCI mode and the diesel combustion mode, and
wherein the lookup tables are indexed by engine speed and at least one of
actual fuel injection quantity and torque.
8. The system of claim 5 wherein the control module controls
target airflow and fuel injection timing during the diesel combustion to PCI
transition mode and the PCI to diesel combustion transition mode based on
separate target airflow and fuel injection timing lookup tables for each of the
diesel combustion to PCI transition mode and the PCI to diesel combustion
transition mode, and wherein the lookup tables are indexed by engine speed
and at least one of actual fuel injection quantity and torque.

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9. The system of claim 5 wherein the control module controls the
desired fuel quantity during the diesel combustion to PCI transition mode and
the PCI to diesel combustion transition mode based on desired torque, actual
fuel quantity, engine speed, mass airflow, and injection timing.
10. The system of claim 5 wherein the control module controls the
target airflow, desired fuel injection quantity, and desired fuel injection timing
during the diesel combustion to PCI transition mode and the PCI to diesel
combustion transition mode based on at least one of a separate target airflow,
desired fuel injection quantity, and desired fuel injection timing lookup tables
for each of the diesel combustion to PCI transition mode and the PCI to diesel
combustion transition mode, and wherein the lookup tables are indexed by
engine speed and at least one of actual fuel injection quantity and torque.
11. The system of claim 5 wherein the control module controls the
target airflow, desired fuel injection quantity, and desired fuel injection timing
during the diesel combustion to PCI transition mode and the PCI to diesel
combustion transition mode based on desired torque, actual fuel quantity,
engine speed, mass airflow, and injection timing.
12. A method of switching between a premixed compression ignition
mode (PCI) and a diesel combustion mode for diesel engines, comprising;
initiating a switch request to switch between at least one of a
premixed compression ignition (PCI) mode and a diesel combustion mode
based on engine speed and at least one of fuel quantity and torque;
commanding at least one of the PCI mode and the diesel
combustion mode based on the switch request; and
controlling at least one of target airflow, desired fuel quantity,
and desired fuel injection timing based on the commanded mode.

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13. The method of claim 12 further comprising determining an
airflow status based on airflow operating conditions of the engine and wherein
the commanding the at least one of the PCI mode and the diesel combustion
mode is based on the airflow status.
14. The method of claim 13 comprising commanding at least one of
a diesel combustion to PCI transition mode and a PCI to diesel combustion
transition mode after initiating the switch request.
15. The method of claim 12 comprising:
determining the target airflow based on the mode, engine speed,
and at least one of actual fuel quantity and torque; and
determining the fuel injection timing based on the mode, engine
speed, and at least one of actual fuel quantity and torque.
16. The method of claim 14 comprising determining the desired fuel
quantity based on desired torque, engine speed, mass airflow, injection
timing, and at least one of actual fuel quantity and torque when the mode is
commanded to the diesel combustion to PCI transition mode and the PCI to
diesel combustion transition mode.
17. The method of claim 14 comprising determining the desired fuel
quantity during the diesel combustion to PCI transition mode and the PCI to
diesel combustion transition mode, wherein the determining comprises:
estimating a torque value based on the current combustion
mode, actual fuel quantity, mass airflow, injection time, and engine speed;
determining a difference between the estimated torque and a
desired torque;
determining a fuel adjustment value based on the difference and
engine operation parameters; and

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adding the fuel adjustment value to the actual fuel quantity to
achieve the desired fuel quantity.
18. The method of claim 13, the determining the airflow status is
further based on at least one of engine speed, fuel quantity, torque, mass
airflow, boost pressure in an intake manifold of the engine, temperature in the
intake manifold, and exhaust pressure.
19. The method of claim 13, the determining of airflow status
comprising:
estimating a percentage of exhaust gas recirculation (EGR)
flowing into an intake manifold of the diesel engine;
estimating a percentage of oxygen in the intake manifold;
computing a target exhaust gas recirculation level for the intake
manifold;
computing a target of oxygen level for the intake manifold; and
setting the airflow status based on a comparison of the
estimated percentage of EGR and the target EGR and a comparison of the
estimated percentage of oxygen and the target oxygen.
20. The method of claim 12 comprising:
determining the target airflow based on the mode, engine speed,
and at least one of actual fuel quantity and torque; and
determining the desired fuel quantity based on the mode, engine
speed, and at least one of actual fuel quantity and torque.
21. The method of claim 12 comprising:
determining the desired fuel quantity based on the mode, engine
speed, and at least one of actual fuel quantity and torque; and
determining the desired fuel injection timing based on the mode,
engine speed, and at least one of actual fuel quantity and torque.

A combustion mode switching control system for diesel engines is
provided. The system includes: a switch determination module that initiates a
switch request to switch between at least one of a premixed compression
ignition (PCI) mode and a diesel combustion mode based on engine speed
and at least one of fuel quantity and torque; a transition module that
commands the at least one of the PCI mode and the diesel combustion mode
based on the switch request; and a control module that controls at least one
of target airflow, desired fuel quantity, and desired fuel injection timing based
on the command.